Microphones for Television
by Lev Orlov

Since "The Audioproducer" detached, reviews on sound equipment in "625" has become a rarity. But let the readers not deceive themselves into believing that either in the context of our periodical's research area or in TV's everyday practice scoring is of somewhat secondary importance despite the fact that phrases like "For Heaven's sake take it away from the scene!" will quite often be heard on shooting stages (Here, as a rule, "it" refers to a microphone).

Should it come to moving microphones away from a sound source, you don't necessarily have to obey referring to subjective sound deterioration from which some TV-viewers would suffer. But don't you ever try to estimate the number of them and the degree of influence it would have on your TV-program ratings; you'd better point out the discrepancy between the "picture's dictatorship" and new tendencies of the TV industry.

Firstly, interviews with state officials of various ranks allow to suppose transition into digital broadcasting will some day come true even in our "individually taken" country. This will apparently lead to changes in quality standards, including those of a sound signal following the picture. Anyway, as they say in Russia: "He, who is warned, is armed".

Secondly, the compromises to gain necessary and sufficient sound quality at shooting were all long ago found. For those who might still wish to follow them the price of the question is time spent for reading special reference literature or at least this very review. And what's left to do is not to mix up useful "information signal" with advertising "noise".

Heritage

Television, unlike cinema, has never been silent and as far back as at birth it got quite enough "dowry", particularly, the same microphone types which had been used in cinema production, sound recording, concert activity as well as radio broadcasting. We won't concentrate upon carbon-, ribbon- and crystal-type microphones for they have a number of disadvantages principally incompatible with TV production. We won't waste our time on detailed description of differences in principals of sound-electricity transformation, either; for those interested I'd recommend an article by A. Veitsenfeld in "The Audioproducer", year 2000, #1 (http://www.625-net.ru/archive/z0100/r1.htm). Having noted, that in TV production only electrodynamic and electrostatic microphones are used, we will determine, within the limits of the article, the peculiarities of their application in certain conditions and stages of work with the terminology, the lack of standardization of which often results in confusion.

Dynamic microphones

This is electrodynamic microphones for short: the etymology emphasizes the process of movement (from eng. or lat. dynamic) of a diaphragm with a coil in a magnetic field. As applied to television, dynamic microphones have both their specific advantages and disadvantages.

The use of big number of different types of the microphones within talk-show

On the one hand, EMF (electromotive force) is produced by means of direct sound pressure transformation and to gain an acceptable voltage at the output for direct connection to a camcorder's audio inputs this pressure must be quite high. On the other hand, direct sound-electricity transformation produces less distortion and electronic noise. "Dynamics" have a relatively heavy, massive body and design tough enough not to 'die' after a couple of falls. Thanks to simplicity of the mechanical part dynamic microphones are less subjected to moisture and temperature fluctuations. Massiveness of the diaphragm causes distortion of the gain-frequency characteristic at highs, in general, and at the edges of a given signal, in particular, yet it plays its positive role, too: the less the distortion when working with loud sounds, the less the risk the feed-back would appear and the less the sensitivity to noise when moving microphones. That's particularly important when recording interviews.

On-camera microphone

Generally speaking, "dynamics" are good when working with quite bright and vivid sounds but they're incapable of handling soft and low ones. This fact limits their application area on TV: they are ideal for reporting and talk-shows but won't go for, say, post-production.

"Rush for profits" makes manufacturers turn towards TV-men: they, for instance, paint dynamic microphone bodies dark or coat them mat and non-reflective.

Finally, dynamics are cheaper, and nobody says the sound going out of a "TV-box" should by all means be gorgeous. The TV-viewers scarcely need to distinguish "all the richness of inflexions and shades" in a reporter's or a talk-show stand "sitter's" voice.

Electrostatic microphones

Among electrostatic microphones they distinguish condenser and electret/back-electret ones, but in specifications just the latter may be strictly called electrostatic. A DC source with a preamp must necessarily be in an electrostatic microphone's path to conform the microphone cap's output to the load's input. 48 up to 200 VDC are used in a condenser for both diaphragm polarization and preamp powering; in electret microphones, voltage (as a rule, lower in tension) is necessary only for preamp powering. Yet it cannot be considered the pivotal aspect to make a choice among electrostatic microphones at various working stages on TV, it's just differences in design and acoustic sensitivity (directivity).

And now let's launch into a little digression concerning terminology. Both manufacturers and resellers may use in specifications the following synonyms of "directivity": "directivity diagram", "directivity characteristic", polar pattern, polar diagram, polar response, sometimes polar response curve, directivity, directionality and others. The manufacturers will by all means give graphs, and as for the dealers, they would in most cases mention directivity briefly.

All above-mentioned terms describe changes in the sound gain-frequency characteristic by the source(s deviation from the axis perpendicular to the diaphragm's plane.

On the basis of directivity they distinguish between specialized microphones - with a single polar pattern - and universal electrostatic microphones - with the possibility to choose up to 9 directivity diagrams (from unidirectional cardioid with changing envelopment width up to two-directional). In universal (or studio) microphones, as a rule, big in diameter and light in weight diaphragms are used. Thanks to that these microphones have high sensitivity and practically linear gain-frequency characteristic.

The use of hand-held microphone

And at the same time they are lighter then dynamic ones, that's why they are preferred when using rods and cranes. All that may be related to positive aspects as far as cover shot scorings and sound-studio applications are concerned where working methods are identical with those of traditional sound-recording: artists themselves and a sound-engineer strictly control both common and individual volume levels. But the critical overload of a studio microphone, regardless of its directivity, may lead not only to disgustingly sounding distortions, but also to diaphragm's destruction as well. And it costs pretty much to repair a good condenser. However, studio microphones, due to their specific design, don't go perfectly for a "live" shooting - that's why both program directors and producers are all against using them in, for example, talk-shows.

And now let's take a closer look at microphones with different mechanical and acoustic features that blend with the context of TV-production more precisely.

As for television, it has enriched the sound-industry with quite a number of brand-new microphones, such as "shotguns" and "clips".

Shotgun-type microphones

Specially designed "shotgun"-type microphones are often included in camcorder sets. In Russian press you can come across very funny synonyms, such as "pipe-mics" or "traveling-wave"-type microphones. However, these notions reflect a unique body design; only the latter two have been invented by engineers. In TV-industry these microphones are called "shotguns" because they can be fixed up at a long distance from (2 up to 10m) and as if aiming at a sound source. The distance, at which we can place a shotgun, not exceeding the technical standard limits concerning sound intelligibility, is determined by the microphone's sensitivity. The shotgun's body length may vary from 15 to 1000mm, the longer it is the stronger the sounds coming up from a source located outside the shooting scene are suppressed. These features are indispensable to "grab" the sound within a strictly limited area, at which the camera lens is directed. That's why on TV shotguns are used as camcorder microphones for ENG Electronic News Gathering, in recording dialogs and live background sounds when shooting in the field (for subsequent dubbing) as an alternative to usual microphones if it is impossible to place them at a proper distance from a sound source to get a sufficient signal level.

Shotgun-type microphone scheme

Unlike usual microphones, shotguns receive the sound not on the diaphragm surface, but along the body sound-feeder line, coinciding with the direction to a sound source. The sound-feeder is an acoustically open "feed" that represents itself a metal "pipe" 10 to 30mm in diameter with special slot holes placed in circular rows along its full length. The condenser microphone cap is mounted deep inside. Since the sound-wave axial spread velocity is the same both outside and inside the pipe, then, apparently, along the directivity axis, waves penetrating into the sound-feeder through all the slot-like holes will sum up in phase. And vice versa, sound waves, coming up at an angle to the microphone's directivity axis, will differ in phase for in this case their spread velocity inside the sound-feeder will be higher than the axial constituent of the sonic velocity outside. Exactly that is why the shotgun sensitivity beyond the directivity axis - both aside and behind - is minimal.

Modular microphone systems

From the viewpoint of the Quality/Price Ratio it may turn out effective to use on TV modular microphone systems, consisting of a main unit (a preamp/switching module) and changeable microphone heads with different directivity characteristics. Being of the same quality, modular systems are more economical than separate microphones. Having once purchased a main unit and a microphone cap, say, cardioid, to begin with, one may get the others - a "shotgun", unidirectional and figure 8-type later in case of necessity and as a financial position allows. Modular systems are especially adored by technical staff for interconnection with other devices is carried out via the main unit's interface, common for all cap types within the system's limits.

PZM microphones

This comparatively new type of electrostatic microphones becomes more and more popular on TV. There are indeed too many Russian equivalents for PZM (Pressure zone microphone, or boundary microphone): "ieaioao", "oaaeaoea", "iee?ioii a?aie?iiai neiy", and "iee?ioii aaaeaiey". The principal of how PZM microphones work is described in detail in an article by Peter Kondrashin in the very same above-mentioned issue of "The Audioproducer", year 2000, #1 (http://www.625-net.ru/archive/z0100/record.htm). And once again, in favor of this microphone's choice its economy speaks: high sensitivity and hemispherical directivity that allow to simultaneously "take up" voices of all participants of a "discussion-table" or other TV-programs of the kind.

Clip-type microphones

The author believes it to be self-explanatory enough why these tiny yet sensitive condenser or electret microphones are called "clips". However, there's another, not to a jacket's lapel, way to attach these microphones - that is right to the speaker's head. The sound engineer would choose namely the latter, keeping in mind the importance of the overload margin and sounding naturalness (i.e. the importance of placing a microphone as close as possible to an artist's month).

Fixing of clip-type microphone to the dress

And as for the producer, he would choose the former variant in order to get the microphone out of sight. Manufacturers know well that in this case the axis of the highest sensitivity may not be directed to a speaker's mouth hence making clip-microphones mostly unidirectional LPF-embedded. But in most cases for the "picture priority" audio engineers are fully answerable, trying to do something with the noise caused by a microphone rubbing against an artist's clothing (for, in fact, here they have to do with body-worn microphones) and, what is more important, trying to compensate enunciation distinction reduction because of natural resonance of the artist's thorax. This is called "to cut through" and done by boosting necessary frequencies with EQs, but it takes both considerable experience in general and plenty of time in each particular case.

General recommendations

Electrostatic microphones have two principal disadvantages: a high price and a need for powering. There's nothing to be done with the former and as for the latter, one should know the following: an uncontrollable amplitude rise may take place in the sound path at initial powering. That's why, when changing a battery or switching the phantom power source on, the receiving equipment's volume controls should be set to min.

A dynamic microphone, all of a sudden plugged into the very same path won't react to turning phantom power on (for it doesn't require it at all) provided it's been correctly soldered under the balanced scheme. Otherwise it's bound to "die", so it's better to turn the camcorder's and audio mixer's phantom power off just in case when replacing microphones.

Don't side step microphone accessories offered by manufacturers. They are not cheap at all, but it is not a "money forcing-out": sometimes a set including a unidirectional model and a "feature" to create necessary directivity costs less than a separate microphone with that special polar pattern. For post-production dubbing it is recommended to use cardioid microphones - both dynamic (to save money on) and condenser/electret ones. It's worth putting a special, as a rule included, foam cap (windscreen) on the microphone's "head" which reduces both an "explosive" effect when pronouncing the consonant "p" and hissing of "s", "z", Russian "zh" and others.

Generally speaking, placed near the sound source, cardioid microphones are especially sensitive to lower frequencies. You may take advantage of this to make a voice, being recorded, sound more expressive and heartfelt.

In ENG the background sound's presence on a sound-track is rather recommended for it can add a scent of naturalness to the event. The best choice is to use two microphones: supercardioid (even dynamic will do) for the speaker's voice and unidirectional or "figure 8" for the background sound.

Just a few words about impedance (i.e. full resistance). Microphones intended for ENG/EFP must be of low Z (50 to 600 Ohm). The higher the impedance is, the shorter the microphone cable should be, the more thoroughly shielded and grounded it should be, otherwise you can't avoid such unpleasant effects as self-excitation, hum & buzz noise and the sonic spectrum upper-part's loss.

Wireless microphones

Having studied the market range, prices and specifications of modern wireless microphones (radio-systems) one may make a conclusion they're an extremely attractive alternative to their wired analogs fixed on camcorders, held in hands or attached to jacket-lapels that belong to "talking heads". Many of manufacturers offer a respective variety, the radio transmission quality being comparable with both "dynamic" and "condenser" specifications. Less cables, more mobility - it is very important on TV. The price of radio systems available on the market not to a lesser degree depends upon the number of radio transmission channels and a bandwidth a system uses.

This should be determined beforehand. Using UHF-radio systems doesn't require permission of "Gossvyaznadzor" (State Communication Inspection, Russian analog for American FCC). They are cheaper than VHF-systems, but you should keep in mind that soon this frequency range will be taken by Digital TV. That's why right now it is high time to select wireless devices that support very fine frequency-tuning to avoid interference with radio channels already engaged by other users.

By way of conclusion

When completing a TV or radio sound-system a financially authorized and practical-minded manager shouldn't make experiments with equipment being offered by immature resellers, running an aggressive promotion of their production. He'd better consult, as they say, respectable companies despite the fact that their production is more expensive in terms of money. But it is not worth sacrificing such unnoticeable, at first sight, features as durability and stability of technical parameters.

Virtual economy may later turn out material loss.

Especially often this happens to a sound system's elements subjected to extreme mechanical loads. It takes many years to create a good microphone collection and both various brand-names microphones and separate specimens are all subjected to a strict selection.

In return, they work not only for intended purposes but, as the stock grows, enhance the prestige of the TV-company.

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